in Aqueous Solutions - American Chemical Society

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2‑Aminothiazole Functionalized Polystyrene for Selective Removal of Au(III) in Aqueous Solutions Chunhua Xiong,†,* Suguo Zhou,† Xiaozheng Liu,† Qian Jia,† Chunan Ma,‡ and Xuming Zheng§ †

Department of Applied Chemistry, Zhejiang Gongshang University, Hangzhou 310012, People’s Republic of China State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Zhejiang University of Technology, Hangzhou 310014, People’s Republic of China § Engineering Research Center for Eco-Dyeing & Finishing of Textiles, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018, People’s Republic of China ‡

ABSTRACT: A new chelating resin, polystyrene-2-aminothiazole (PS-AT), was synthesized via one-step reaction by grafting 2aminothiazole in a chloromethylated polystyrene polymer. Its structure was characterized by elemental analysis and infrared spectroscopy. Batch experiments were applied to investigate the adsorption properties of PS-AT for Au(III) ions. The resin exhibits an excellent selectivity for Au(III) ions in the presence of Ni(II), Cu(II), Cd(II), and Co(II) ions. The maximum adsorption capacity obtained at 308 K was 733.8 mg/g. The adsorption kinetic and equilibrium data were well fitted to the pseudo-second-order model and the Langmuir isotherm model, respectively. Desorption of gold from the resin can be achieved using 60 mL of 2 mol/L HCl-10% thiourea solution with a desorption ratio of 93.8%. The XPS data, along with IR spectra, revealed that gold was adsorbed on the surface of PS-AT in the form of chloride, and nitrogen and sulfur were involved in the chelation of gold chloride.

1. INTRODUCTION With specific physical and chemical properties, gold has been widely used in the areas of industry, agriculture, and medicine. Economically, gold is not only used as currency but also as an important investment commodity.1 In consideration of the value and scarcity of gold, it is necessary to recycle and reuse gold from industrial waste. Traditional technologies, such as precipitation, cyanide leaching, filtration, electrochemical treatments, reverse osmosis, ion exchange resins, and evaporation, can be expensive, inefficient, and pollution causing.2,3 What’s more, a typical waste usually contains gold along with the toxic metals such as Cu, Co, Cd, and Ni,4 which has spurred the intensive study of adsorbents with efficient selectivity to recover precious metals from waste solutions. Chelating resins containing functional groups were extensively used to treat waste metals in a trace or ultra concentration range because of its low cost, high adsorption capacity, good recovery, and excellent selectivity.5−8 The synthesis polymers containing heterocyclic functional groups, such as imidazole,9 bis(2-benzimidazolyl methyl)amine,10 pyrimidine,11 pyridine,12 quinoline,13 and 2-amino-2-thiazoline,14 have been successfully applied to the removal of trace metals. Macroporous chloromethylated polystyrene beads (PSCl) are an ideal polymeric matrix with stable mechanical properties. The active chloromethyl group in PS-Cl can be easily converted into a number of new functional groups via special reactions. These structural characteristics are attractive for developing adsorbents for metal ions.15−20 Chelating resins containing subgroups with sulfur or nitrogen atoms can be used in the selective removal of precious metals.21,22 In this work, a selective chelating resin, chloromethylated polystyrene modified by 2-aminothiazole groups containing both nitrogen and sulfur, was used in selective adsorption of © 2014 American Chemical Society

gold from the mixed metal solutions containing copper, cobalt, cadmium, and nickel. The adsorption capability for Au(III) in the aqueous solution had been investigated by a series of batch experiments. To further understand the gold adsorption process, the adsorption kinetics, isotherms, and the thermodynamic properties of adsorption of Au(III) on the synthetic resin were also clarified. FT-IR and XPS analysis was applied to the investigation of the adsorption mechanism. Finally, the recovery of gold was also studied in detail.

2. MATERIALS AND METHODS 2.1. Materials. Macroporous chloromethylated polystyrene beads (PS-Cl for short) with a degree of cross-linking of 8% DVB, a chlorine content of 19.15%, and a specific surface area of 43 m2/g were purchased from the Chemical Factory of Nankai University (China). 2-Aminothiazole (AT) was produced by Merck-Schuchardt. In the experiments AuCl3· HCl·4H2O, NiCl2·6H2O, CuCl2·2H2O, ZnCl2·6H2O, CdCl2· 4H2O, and CoCl2 were respectively used to produce Au(III), Ni(II), Cu(II), Zn(II), Cd(II), and Co(II) solutions, All other reagents and solvents herein were of analytic grade and used without further purification. 2.2. Apparatus. Infrared spectra of the resins were scanned in the region of 400−4000 cm−1 in KBr pellets on NICOLET 380 FT-IR spectrophotometer; The elemental analysis was carried out using a Vario EL III Elemental Analyzer; Thermogravimetric analysis in a range of temperature 50−1000 °C by 20 °C min−1 under the protection of nitrogen on a TGA/DSC1 Received: Revised: Accepted: Published: 2441

October 17, 2013 January 14, 2014 January 22, 2014 January 22, 2014 dx.doi.org/10.1021/ie403502r | Ind. Eng. Chem. Res. 2014, 53, 2441−2448

Industrial & Engineering Chemistry Research

Article

instrument; X-ray photoelectron spectroscopy (XPS) of the resins were obtained with an ESCALab220i-XL electron spectrometer from VG Scientific using 300W AlKα radiation. The base pressure was about 3 × 10 −9 mbar. The concentrations of gold metal ions and the foreign metal ions were determined by ICP-AES. The sample was shaken in the DSHZ-300A temperature constant shaking machines. Water obtained through a Molresearch analysis-type ultrapure water machine was used in the present work. 2.3. Preparation of the Chelating Resin PS-AT. A certain amount of PS-Cl were swollen in 300 mL of the reaction solvents in a 500 mL three-neck round-bottom flask overnight. Then, a certain amount of 2-aminothiazole (AT) and metallic sodium used as catalyst were added into the flask. The system was degassed by bubbling it with a high purity nitrogen flow to remove air, and then the reaction mixture was reacted with stirring under nitrogen atmosphere at different temperatures for 13 h. After reaction, the resin was washed thoroughly with the reaction solvents, deionized water, ethanol, acetone, and ether successively. The resin was dried at 50 °C under vacuum for analysis. N,N-Dimethylformamide (DMF) 2.16 and 1,4-dioxane were selected as the reaction solvents. The PS-Cl used in the synthesis experiment was 1 g. The amount of 2-aminothiazole with different molar ratio (AT/Cl = 1:1, 2:1, 3:1, 4:1, 5:1, 6:1) was 0.54 g, 1.08 g, 1.62 g, g, 2.7 g, and 3.24 g, respectively. The study of temperature in the reaction system was 40, 60, 80, 100, and 120 °C. The percentage conversion of the functional group of the chelating resin synthesized can be calculated from nitrogen content with the following equation: Fc =

Seli = log

E(%) =

C0 − Ce V WCe

CdVd × 100 (C0 − Ce)V

(5)

3. RESULTS AND DISCUSSION 3.1. Synthesis and Characterization of PS-AT Resin. 3.1.1. Selectivity of Reaction Conditions. The synthesis conditions, such as reaction solvents, molar ratio, and reaction temperatures, were investigated, and the optimal synthesis conditions were determined according to N content (N%) and functional group conversion (FGC, %). Reaction solvent has an effect on the swelling property of the polymer matrix and the permeability of ligand. Compared with 1,4-dioxane, a higher N content (6.905%) was obtained with the selected DMF as the reaction solvent under the conditions of 100 °C, 13 h, and a molar ratio of 4:1. This is possibly due to the better swelling property of PS-Cl beads and permeability of AT in DMF than that in 1,4-dioxane. Therefore, DMF was selected as the reaction solvent. The effects of molar ratio and temperature on the synthesis process are shown in Figures 1 and 2, respectively. The maximum of the nitrogen content (7.069%) and the functional group capacity (2.52 mmol FG/g) of PS-AT resin were obtained under the optimal conditions, i.e., DMF as reaction solvent, molar ratio of AT to PS-Cl at 5:1 (Figure 1) and reaction temperature of 100 °C (Figure 2).

where F0 (5.39 mmol of Cl/g) is the functional group capacity of PS-Cl; Fc is the content of the functional group of PS-AT resin (mmol/g); x is the functional group conversion (%); nN is the number of nitrogen atoms of ligand molecules; Nc is the nitrogen content of the PS-AT resin (%); and 14.01, M1, and M2 are the weight of nitrogen, AT, and HCl (mol/g), respectively. 2.4. Adsorption Experiments. 2.4.1. Batch Studies. Batch studies were carried out by shaking 0.01 g dry PS-AT resin with 60 mL of the studied metal ions in a shaker at 100 rpm at the desired initial concentration, pH, constant temperature, and contact time. The pH was adjusted using HCl solutions. The concentration of metal in each sample was measured by ICPAES. Kinetic study was carried out with an initial concentration of Au(III) of 0.1593 mg/mL. Isotherm study used a different initial concentration of Au(III) ranging from 0.1275 mg/mL to 0.1753 mg/mL. The selectivity of PS-AT toward Au(III) was carried out in a mixed system containing Au(III), Co(II), Cd(II), Ni(II), and Cu(II) ions. The adsorption capacity (Q, mg/g), distribution coefficient (D, mL/g), and the adsorption selectivity were calculated with the following formulas:

D=

(4)

where Cd is the concentration of the solutes in the desorption solutions; Vd is the volume of the desorption solution; and C0, Ce, and V are the same as defined above.

(1)

C0 − Ce V W

(Q e/Ce)j

where C0 is initial concentration in solution (mg/mL), Ce is equilibrium concentration in solution (mg/mL), V is solution volume of solution (ml), W is resin dry weight (g), and Qe is the equilibrium adsorption capacity (mg/g). The index i pertains to Au(III) and index j refers to the foreign metals. 2.4.2. Desorption Studies. The gold-loaded resin (PS-ATAu) was placed in the iodine flasks, and then 60 mL of thiourea was added. The HCl/thiourea solutions with different concentrations and acidities were further stirred at 100 rpm for 24 h at 298 K. After desorption, the final Au (III) ion concentrations in the aqueous phase were determined by ICPAES. The desorption ratio (E) was calculated from eq 5:

Nc × 1000 1 × F0x = 14.01 × nN 1 + [1 × F0x(M1 − M 2)]/1000

Q=

(Q e/Ce)i

(2) Figure 1. Effects of the molar ratio of reagent of AT/Cl on N content and the percentage conversion of functional group, 13 h, DMF, 100 °C.

(3) 2442

dx.doi.org/10.1021/ie403502r | Ind. Eng. Chem. Res. 2014, 53, 2441−2448


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Scheme 1. Potential Synthesis Routes for PS-AT Resin

complex of gold is AuCl4− at low pH below 3.0. −NH− as the subgroup of the new synthetic resin (PS-AT) may be protonized in acidic medium to change into −NH2+−.14 As presented in Figure 4, the adsorption capacity of PS-AT was Figure 2. Effects of reaction temperature on N content and the percentage conversion of functional group, 13 h, DMF, AT/Cl = 5.

3.1.2. FT-IR Spectra. The FT-IR spectra of PS-Cl, AT, PSAT, and gold-loaded PS-AT (PS-AT-Au) are shown in Figure 3. As compared with the curve of PS-Cl, the characteristic peaks at 1263 and 672 cm−1, which are assigned to CH2−Cl, disappeared as expected. In the spectra of PS-AT, the characteristics bands of −NH2 at 3411 and 3289 cm−1 disappeared, whereas a strong and broad characteristic band of secondary amine (N−H) peak at 3433 cm−1 and the antisymmetric stretching vibration band at 2924 cm−1 and symmetric stretching vibration band at 2853 cm−1 of −CH2 groups appeared, which confirmed that the reaction between the CH2−Cl and −NH2 group occurred. In addition, the νC−N at 1358 cm−1, νCN at 1628 cm−1, and νC−S at 719 cm−1 belonging to thiazole rings also appeared in the spectra of PSAT, which can be further confirmed by the fact that the AT ligands have grafted on the PS-Cl polymer to form PS-AT resin.23−26 According to the IR spectra in Figure 3, the proposed structure of the new synthetic resin is presented in Scheme 1. 3.2. Effect of pH. The form of the metal ions and the surface properties of the adsorbents can be seriously affected by the solution pH.27 According to Ogata,28 the predominant

Figure 4. Effect of pH on the adsorption capability of PS-AT for Au(III) (resin 0.01g, initial Au(III) concentration = 9.56 mg/60.0 mL, T = 298 K, 100 rpm, 144 h, initial pCl = pH).

significantly affected by the solution pH and showed a decreasing trend with low pH due to the complete adsorption between AuCl4− and Cl− on the surface of protonized PS-AT resin. When the pH was 2.6, the adsorption capacity of Au(III) ions on PS-AT reached the maximum value of 649.8 mg/g, similar to the initials reports by Donia et al.29 and Chen et al.30

Figure 3. IR spectra of the PS-Cl, AT, PS-AT, and Au(III) loaded PS-AT. 2443



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and N− group of thiazole in the resin. After gold adsorption, the N1s band was shifted to 397.5 eV, due to the formation of bonds between the nitrogen and the gold. The S 2p peak of PSAT resin in Figure 6b displays a significant intensity decrease and shift toward higher binding energy after gold adsorption, indicating that a complex between gold and sulfur occurred. The Au 4f spectra shown in Figure 6c is typical for gold, binding energies of 87.8 and 91.3 eV, corresponding to Au 4f7/2 and Au 4f5/2, confirming the adsorption of AuCl4− in the resin, the Au 4f7/2 shift from 87.8 to 85.4 eV, and the Au 4f5/2 shift from 91.3 to 88.9 eV due to the complex between sulfur, nitrogen, and gold.33 The atomic content of N 1s, S 2p, Cl 2p, and Au 4f before and after gold adsorption on PS-AT resin is shown in Table 1. It can clearly be seen that the atomic content of Cl 2p increased, evidently from 6.35% to 27.87%, whereas the atomic content of N 1s and S 2p decreased after gold adsorption. It may be speculated that the gold adsorption on the surface of the resin is in the form of chloride, the existence of gold chloride contributes to the increase in atomic content of Cl 2p. 3.4. TGA Analysis. The thermo-gravimetric analysis (TGA) was used to study the thermal stability of the PS-AT resin before and after adsorption of Au(III), and the TGA curve obtained is illustrated in Figure 7. Hardly any loss of weight can be observed for the resin before and after gold adsorption in the range of 25−185 °C, which demonstrates that the adsorption process on the PS-AT can be carried out at a high temperature. Then, two decomposition steps occurred: one is from 185 to 435 °C, and the other one is from 435 to 565 °C. The higher residue (58.8%) of PS-AT-Au compared with that of PS-AT (39.5%) further revealed that Au(III) ions were adsorbed onto PS-AT. 3.5. Adsorption Kinetics. In order to find out the equilibrium time for the maximum adsorption and to determine the rate limit step of the adsorption process, the change in the adsorption capacity of Au(III) on the resin at different times was recorded. The results are shown in Figure 8. It can be seen in Figure 8 that the equilibrium state was not reached for 96 h. And as the temperature increased from 288 K to 318 K, the equilibrium adsorption capacity exhibited the same trend. A higher adsorption capacity at higher temperature suggests that the Au(III) adsorption onto the PS-AT resin is a temperaturedependent process.24 To further investigate the rate-controlling step of the Au(III) adsorption process, the Lagergren first-order and pseudosecond-order adsorption model were utilized. The following eqs 634 and 735 express the Lagergren first-order and pseudosecond-order model, respectively:

When the pH was above 2.6, a slight decrease of adsorption capacity occurred for the increasing OH− in solution compete with Cl− and form hydroxo-containing gold complex.27 The effect of pH on gold adsorption from the mixed solutions containing copper, cobalt, cadmium, and nickel ions was also investigated, and the results are shown in Figure 5. It

Figure 5. Effect of pH on the adsorption capability of Au(III), Cu(II), Ni(II), Cd(II), and Co(II) (resin 0.01 g, initial Au(III) concentration = 5.736 mg/60.0 mL, the other metal ion concentration 12 mg/60.0 mL, T = 298 K, 100 rpm, 144 h, and the chloride concentration is the sum of the amount of hydrochloric acid and metal chloride).

can easily be seen that PS-AT adsorbed trace amounts of copper, cobalt, cadmium, and nickel over the range of study of pH from 0.4 to 2.8, and the adsorbed gold gradually increased to 550 mg/g when the pH reached 2.0. The resin’s selectivity for gold adsorption over copper, cobalt, cadmium, and nickel according to eq 4 in the range from 0.914 for pH 0.4 to 3.43 for pH 2.8, exhibiting a high separation ability in the pH region of above 2.0. Since the pH of gold wastewater from the electroplating industry typically is in the range of 2−3,31,32 the proposed application scope for PS-AT resin at pH 2.0−2.8 is a matter of practical importance, and Au(III) ions can be easily separated from these metal matrix. Compared with the single gold adsorption system, a serious decline adsorption capacity for Au(III) from the binary solution can be observed in Figure 5 (cf., Figure 4) over a pH range of 1.0−2.8. It is possible because the addition of chloride metal salts exacerbated the competition between chloride ions and AuCl4−. 3.3. FT-IR and XPS Analysis. The adsorption mechanism of gold on the surfaces of PS-AT resin was investigated by FTIR and XPS analysis. In the spectra of PS-AT-Au (Figure 3), the νC−N, νCN, and νC−S stretching bands were shifted to a lower wavenumber by 13 cm−1 (from 1358 to 1345 cm−1), 17 cm−1 (from 1628 to 1611 cm−1), and 12 cm−1 (from 719 to 707 cm−1), respectively, suggesting that the nitrogens and sulfur in the thiazole ring were involved in Au(III) adsorption. In addition, the νN−H stretching band decreased and shifted slightly (from 3433 to 3438 cm−1), indicating that the secondary amine is also available in the Au(III) binding process. XPS analysis was performed to investigate the molecular level information of gold adsorption on the PS-AT resin containing aminothiazole ligands. The results obtained are shown in Figure 6. Figure 6a shows the XPS N ls spectra. Before gold adsorption, the N1s binding energy located at 397.2 eV is composed of a signal, which belongs to the nitrogen in −N−H,

log(Q e − Q t) = log Q 1 − t 1 t = + 2 Qt Q2 k 2Q 2

k1 t 2.303

(6)

(7)

where Qe and Qt are the adsorption capacities at equilibrium and at various time (mg/g); Q1 and Q2 are the calculated adsorption capacities of the Lagergren first-order model and the pseudo-second-order model (mg/g), respectively; and k1 and k2 are the rate constants of the Lagergren first-order model (h−1) and the pseudo-second-order model (g/(mg·h)). The kinetic parameters are represented in Table 2. A higher value of correlation coefficients (R22), along with good agreement of calculated Q2 with experimental data, indicates that the 2444



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Figure 6. XPS spectra of PS-AT not subjected and subjected to Au(III) adsorption (a) N1s, (b) S2p, and (c) Au4f (adsorption conditions: resin 0.01g, initial Au(III) concentration = 9.56 mg/60.0 mL, T = 298 K, 100 rpm, initial pH 2.6, initial pCl 2.6, 144 h, before XPS analysis washed by deionized water and then dried at 50 °C under vacuum).

Ce C 1 = e + Qe Qm bQ m

Table 1. Atomic Content(%) of the PS-AT before and after Adsorption PS-AT PS-AT-Au

N 1s

S 2p

Cl 2p

Au 4f

70.61 48.32

23.04 13.14

6.35 27.87

10.67

log Q e = log K f +

1 log Ce n

(8)

(9)

where Qe is the equilibrium adsorption capacity, Ce is the equilibrium concentration, Qm is the maximum adsorption capacity of Langmuir, b is Langmuir constant, n is a Freundlich constant associated to the adsorption intensity, and Kf is roughly an indicator of the adsorption capacity. The Langmuir and Freundlich isotherm constants were computed and listed in Table 3. Obviously, with a higher R2 value, the Langmuir model was found to be a better fit for the experiment data than the Freundlich model. The results demonstrated that the adsorption of Au(III) ions on PS-AT is of a monolayer type,

adsorption process can be better explained by pseudo-secondorder mechanism, which means the Au(III) adsorbed on PS-AT is controlled by chemisorption.36 3.6. Adsorption Isotherms. To further explore the adsorption mechanism, collected adsorption data at three different temperatures in the preferred pH of 2.6 were fitted with two common adsorption model: Langmuir37 and Freundlich38 isotherm models. The linear form of the Langmuir and Freundlich model equation are formulated as follows: 2445



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Table 3. Parameters for Adsorption Isotherms of Au(III) by PS-AT Qm T (K) (mg/g) 288 298 308

Figure 8. Adsorption kinetics and capacity Q at different times and different temperatures (resin 0.01 g, initial Au(III) concentration = 9.56 mg/60.0 mL, initial pH 2.6, initial pCl = 2.6, 100 rpm).

(10) (11)

ΔG = ΔH − T ΔS

b (mL/mg)

R2

1/n

R2

78.6 107.8 248

0.9804 0.9883 0.9996

0.19 0.14 0.12

896.4 915.8 1070.8

0.7101 0.7527 0.9413

4. CONCLUSIONS In this research, a new chelating resin containing a thiazole moiety has been successfully synthesized by grafting 2aminothiazole (AT) onto chloromethylated polystyrene beads via one-step reaction. IR and XPS analysis strongly suggests that gold in the form of chloride adsorbed on PS-AT via complexation and ion exchange. The adsorption process follows a pseudo-second-order model, suggesting that chemisorption is the rate-controlling step. This fits well with the Langmuir isotherm, indicating that the monolayer adsorption is dominant. Thermodynamic parameters obtained indicate that the Au(III) adsorbed on PS-AT is spontaneous and endothermic in nature. In a word, the results obtained from the present investigation confirm that PS-AT resin can be used in the selective removal of Au(III) ions from aqueous solutions with an excellent adsorption capacity (733.8 mg/g at 308 K),

where interactions between adsorbed molecules are negligible.39 3.7. Thermodynamic Parameters. The thermodynamic properties were studied by allowing 0.01 g dry PS-AT to equilibrate with 60 mL of Au(III) solutions (9.56 mg/60 mL) under 288, 298, and 308 K with an initial solution pH of 2.6. Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) for the Au(III) adsorption were calculated by the following equations:40 ΔH ΔS + 2.303RT 2.303R

Freundlich Kf((mg/g)/ (mg/mL)1/n)

negative value of ΔG (kJ/mol) (288 K, −21.5; 298 K, −23.4; 308 K, −25.3) indicates that the gold adsorbed on the PS-AT resin is feasible and thermodynamically spontaneous. The decrease in magnitude of ΔG as the temperature rises from 288 K to 318 K confirms that the adsorption is favorable at higher temperatures, due to the greater swelling of the resin and increased diffusion of metal ions into the resin.41 The positive value of ΔH = 33.6 kJ/mol suggests that the gold adsorption is an endothermic process. In addition, the positive value of ΔS = 191.3J/(K mol) confirms that randomness increased at the adsorbent−adsorbate interface during the adsorption of Au(III), which suggests that the adsorption is an entropydriven process.41,42 3.8. Desorption Experiment. A desorption experiment was carried out to study the recovery of the adsorbed gold. HCl-thiourea solutions are usually used in the desorption process to recover gold from adsorbents.1,43,44 It was observed in Table 4 that Au(III) could be easily desorbed with 60 mL of 2 mol/L HCl-10% thiourea with a desorption ratio of 93.8%. Table 5 lists the gold adsorption and selectivity about a series of adsorbents, and the desorption ratio was reported in the literature.3,28,30,45−49 It can be seen that a material with good comprehensive properties (high adsorption capacity, high selectivity, and high recovery rate) toward gold was seldom reported, PS-AT resin can potentially be used as an efficient gold recovery material with a good adsorption capacity, a high selectivity, and a high desorption rate.

Figure 7. TGA curves of PS-AT and Au(III) loaded PS-AT.

log D = −

636.1 713.8 806.5

Langmuir

where D is the distribution coefficient, R is the gas constant (8.314 J/(mol K)), and T is the absolute temperature (K). The

Table 2. Kinetics Models Constants for Adsorption of Au(III) by PS-AT Lagergren first-order model

pseudo-second-order model

T (K)

Qe (mg/g)

k1 (h−1)

Q1 (mg/g)

R12

k2 (g/(mg·h)

Q2 (mg/g)

R22

288 298 308

565.8 635.4 733.8

3.2 × 10−2 4.3 × 10−2 4.8 × 10−2

431.7 473.0 519.3

0.9865 0.9823 0.9818

1.2 × 10−4 1.8 × 10−4 1.8 × 10−4

625.0 666.7 769.2

0.9913 0.9971 0.9977

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Table 4. Desorption of Au(III) by Different Eluents at 298 K eluent

1% thiourea

5% thiourea

1 M HCl-1% thiourea

2 M HCl-5% thiourea

2 M HCl-10% thiourea

desorption ratio (%)

53.5

66.7

60.3

78.6

93.8

Table 5. Gold Adsorption and Desorption from Single and Binary Solutions

a

adsorbent

Au capacity (mg/g)a

PANI-EHL tannin gel chitosan silk TF resin UF resin PS-APD resin carbon (barley straws) carbon (rice husks) NH2−MCM-41 ODPA-BH PS-AT resin

4193.0 8000 650.0 197.0 29.5 17.7 300.8 289.5 149.7 275 465.16 733.8

selectivityb

desorption ratio (%)

3.10 2.76 1.62 1.40 3.26

3.43

reference 3 28 30 45 46 47

99 92.63 93.8

48 49 this work

Gold adsorption capacity from single solutions. bSelectivity calculated according to eq 4 from mixed solutions. (8) Laatikainen, K.; Laatikainen, M.; Branger, C.; Paatero, E.; Sirén, H. Role of Ligand Acidity in Chelating Adsorption and Desorption of Metal Salts. Ind. Eng. Chem. Res. 2012, 51, 12310. (9) Li, C. X.; Dou, J. T.; Cao, J. J.; Li, Z. Q.; Chen, W. K.; Zhu, Q. Z.; Zhu, C. F. A Novel Chelating Organosilic One Resin Bearing Long Chain Imidazolyl Ligands: Preparation, Characterization, And Adsorption Properties. J. Organomet. Chem. 2013, 727, 37. (10) Pramanik, S.; Dhara, P. K.; Chattopadhyay, P. A Chelating Resin Containing Bis(2-benzimidazolylmethyl)amine: Synthesis and MetalIon Uptake Properties Suitable for Analytical Application. Talanta 2004, 63, 485. (11) Gutiérrez-Valero, M. D.; Godino-Salido, M. L.; ArranzMascarós, P.; López-Garzón, R.; Cuesta, R.; García-Martín, J. Adsorption of Designed Pyrimidine Derivative Ligands on an Activated Carbon for the Removal of Cu(II) Ions from Aqueous Solution. Langmuir 2007, 23, 5995. (12) Sahana, A.; Das, S.; Banerjee, A.; Lohar, S.; Karak, D.; Das, D. Pyridine Appended L-Methionine: a Novel Chelating Resin for pH Dependent Cr Speciation with Scanning Electron Microscopic Evidence and Monitoring of Yeast Mediated Green Bio-reduction of Cr(VI) to Cr(III) in Environmental Samples. J. Hazard. Mater. 2010, 185, 1448. (13) Jan, M. R.; Shah, J.; Sadia, M.; Haq, A. Preconcentration and Determination of Pb(II) in Aqueous Samples Using Functionalized Dowex 1 × 8. Solvent Extr. Ion Exch. 2012, 30, 306. (14) Chen, Y. Y.; Zhao, Y. Synthesis and Characterization of Polyacrylonitrile-2-amino-2-thiazoline Resin and Its Sorption Behaviors for Noble Metal Ions. React. Funct. Polym. 2003, 55, 89. (15) Xiong, C. H.; Yao, C. P. Synthesis, Characterization and Application of Triethylenetetramine Modified Polystyrene Resin in Removal of Mercury, Cadmium and Lead from Aqueous Solutions. Chem. Eng. J. 2009, 155, 844. (16) Xiong, C. H.; Chen, X. Y.; Yao, C. P. Preparation of a Novel Heterocycle-Containing Polystyrene Chelating Resin and Its Application for Hg(II) Adsorption in Aqueous Solutions. Curr. Org. Chem. 2012, 16, 1942. (17) Zong, G. X.; Chen, H.; Qu, R. J.; Wang, C. H.; Ji, N. Y. Synthesis of Polyacrylonitrile-Grafted Cross-Linked N-Chlorosulfonamidated Polystyrene via Surface-Initiated ARGET ATRP, and Use of the Resin in Mercury Removal after Modification. J. Hazard. Mater. 2011, 186, 614. (18) Qu, R. J.; Wang, C. H.; Sun, C. M.; Ji, C. N.; Cheng, G. X.; Wang, X. Q.; Xu, G. Syntheses and Adsorption Properties for Hg2+ of Chelating Resin of Crosslinked Polystyrene-Supported 2,5-Dimercapto-1,3,4-thiodiazole. J. Appl. Polym. Sci. 2004, 92, 1646.

high selectivity (2.45 to 3.43 from pH 2 to 2.8), and a good recovery rate (93.8%).

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-0571-88071024-7571. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work is supported by the National Science Fundamental Project of China (No. 20972138), the Key Laboratory of Advanced Textile Materials and Manufacturing Technology (Zhejiang Sci-Tech University), the Ministry of Education (No. 2013006), and the State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology (GCTKF2012009).

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REFERENCES

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